How can i make a proper light inside a circle with objects so their surface is illuminated?
The light sources can be invisible to the camera. Set Cycles Ray Visibility to FALSE

You mentioned trick.  Consider the point light external to the sphere.  Set Cycles Ray Visibility to FALSE.  Each planet has a sister light planet not visible to the camera.  They can both rotate relative to Sun. You may consider [Tracking] Constraint.
The Sun. Set Cycles Ray Visibility to FALSE.